<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>sky-gradient</title>
</head>
<style>
  html, body {
    width: 100%;
    height: 100%;
    margin: 0;
    padding: 0;
    background: #00000c;
    overflow: hidden;
  }
  .sky-gradient {
    position: relative;
    z-index: 1;
    float: left;
    width: 4%;
    height: 20%;
    cursor: pointer;
  }
  .sky-gradient::after {
    content: "";
    position: absolute;
    top: 100%;
    width: 2500%;
    height: 400%;
    background: inherit;
    transform: translateZ(0);
    opacity: 1;
    animation: fadeIn 2s ease-out;
  }
  @keyframes fadeIn {
    from { opacity: 0; }
    to { opacity: 1; }
  }
  .sky-gradient-18 {
    background: linear-gradient(to bottom, #154277 0%, #576e71 30%, #e1c45e 70%, #b26339 100%);
  }
</style>
<body>
<div class="sky-gradient sky-gradient-18">18</div>
</body>
</html>
